To improve the expressivity and accuracy of database query interfaces, a keyword-based constrained query language is introduced to let users explicitly express the intent of their search using keywords linked by meaningful grammatical connectives. Individually, keywords and connectives correspond to textual descriptions attached to components of the database graph schema, and as a whole, a so-called connected keywords query corresponds to a textual description of an SQL query. The translation process of such a query into SQL is mainly composed of two steps: first, the syntactic structure of the keyword query is analyzed to exhibit projection and selection statements using predefined graph patterns, then non explicit joins are deduced to obtain a complete translation of the keyword query as a meaningful connected subgraph. Experimentations show the relevance of the approach in terms of expressivity and efficiency.